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Causes of second trimester loss

In this section we list the main known causes of second trimester loss. Some can cause earlier losses too. Others may cause a problem after 24 weeks of pregnancy as well as before.

You may never know what caused your loss, but it’s important to know that it is very unlikely to be due to anything you did or didn’t do.  Most miscarriages, at whatever stage, happen because of a problem in the baby’s development.

Chromosome or genetic abnormalities

A baby’s chromosomes are formed when the egg and sperm meet at conception. The baby receives half its chromosomes from each parent. Sometimes things can go wrong at this time and may result in the baby having the wrong number of chromosomes, or an individual chromosome may be too long or too short.

This can cause an abnormality which may cause an early miscarriage, but sometimes the baby dies later in pregnancy or shortly after birth.  However, some babies with genetic or chromosome abnormalities survive.

Examples of chromosome or genetic abnormalities are Downs Syndrome, Patau Syndrome, Edwards Syndrome and Turner Syndrome.

If a chromosome abnormality is suspected as a cause of a loss, it may be possible to confirm this, or rule it out, by checking the baby’s chromosomes from blood, skin or the placenta.

In most cases a chromosome or genetic abnormality occurs by chance, but occasionally it is inherited from a parent. It is possible to check the parents’ chromosomes through blood tests. This information can help identify the risk of a similar problem happening again.

If there is an increased risk, you may be referred to a specialist to have tests and perhaps given advice about future pregnancies.

Structural abnormalities

These are problems in the baby’s body, for example spina bifida or a congenital heart defect, (when the heart doesn’t form correctly). These are sometimes seen on an ultrasound scan, but sometimes they are only discovered after the baby is born.

If your baby is found to have this kind of problem, you should be offered genetic counselling so that you can find out more about the chances of it happening again.

Problems with your womb (uterus) or cervix

An unusually shaped womb (uterus) can cause a late loss. Doctors sometimes suggest an operation to correct the shape of the womb but this isn’t always possible or recommended.

Problems with the cervix (the neck of the womb) can also cause late loss. The cervix should stay tightly closed during pregnancy. But if it is weakened or damaged for some reason, it may open as the baby grows bigger, causing a very early birth.

If your doctor thinks this might be the reason for your loss, they may suggest that you have a strengthening stitch, called a cervical stitch, in your next pregnancy. This is usually done under a general anaesthetic at 13 or 14 weeks of pregnancy.

The Royal College of Obstetricians & Gynaecologists publishes a very helpful patient leaflet on cervical stitch here.


Some infections can cause a second trimester loss, either by infecting the baby or by infecting the amniotic fluid (the liquid around the baby).

Infections directly affecting the baby include parvovirus, cytomegalovirus (CMV), listeria and toxoplasmosis. Infections like these in one pregnancy do not increase the risk of them happening in a future pregnancy.

Infections of the amniotic fluid can happen when bacteria (germs) that normally live in the vagina get into the womb. One example is bacterial vaginosis (BV), a common infection which has been associated with premature (early) labour.

Antiphospholipid Syndrome (APS)

APS is a condition that increases blood clotting. It is sometimes called “sticky blood syndrome” or Hughes syndrome.

If blood clots too easily during pregnancy, it can cause early or late loss, as well as other pregnancy problems.

If you are found to have APS, you will usually be treated with low-dose aspirin and possibly another blood-thinning drug called heparin in your next pregnancy.

There is more detail in our leaflet Antiphospholipid Syndrome (APS) and pregnancy loss.

Finding out more

Investigations  You may be offered some tests or investigations for you or your baby after your loss and you might need time and more information before making any decisions.  We talk more about investigations here.

Research  Doctors and researchers are continuing to try to understand more about the causes of second trimester loss and very early birth (often called pre-term birth) and whether there are treatments that might help.  You might be asked to help with research because of your experience, either during your loss or afterwards.  In all cases, you should be given clear information about what taking part means and given time to think about whether or not you want to be involved.  It will always be your decision.


On the next page, we talk about signs and symptoms and the physical process of second trimester loss: labour and birth